Cell Membrane Dynamically Regulates The Interaction Between Transmembrane Protein And Its Ligands

Protein-protein interaction,as a key way for proteins to function,plays an important role in cell signal transduction,apoptosis,cell growth,cell proliferation and other processes.And the transmembrane proteins are important components to mediate cell-cell signal transduction and cell environment sensing,which are regulated by the cell membrane microenvironment.Biophysical properties of the cell membrane,such as two-dimensional confinement,bio-mechanical force and membrane potential,can potentially affect the function of transmembrane proteins.Combining patch-clamp technique,FRET imaging,immune electron microscope technology,molecular dynamics simulations,optogenetics,primary hippocampal neurons culture in vitro and SLE clinical data,we used the biophysical methods(bio-membrane force probe and micropipette adhesion frequency assay)to reveal the effect of the cell membrane on transmembrane proteins' function.In the first project,we revealed the alternative splicing effect on neural synaptic adhesion molecule NL1s' synaptogenic ability primarily through in vitro co-culture of primary hippocampal neurons and over-expressing NL1 s 293T cells.Then,the kinetics of different NL1s/NRXN?s splicing variant pair interactions were determined through BFP assay.It shows that alternative splicing couples the two-dimensional confinement and biomechanical environment of the cell membrane to dynamically regulate the NL1s/NRXN?s interaction.Unexpectedly,it simultaneously exists slip bonds,catch bonds and approximate ideal bonds in the different NL1s/NRXN?s splicing variant pair interactions under bio-mechanical forces.Thus,the two-dimensional confinement and biomechanical environment of the membrane can finely tune NL1s/NRXN?s binding kinetics and better regulate the function of NL1s/NRXN?s.In the second project,we primarily discovered that plasma membrane depolarization specifically enhances the interaction of NL1/NRXN3?.In the molecular mechanism,NL1 can sense plasma membrane depolarization through the disordered stalk region to induce the extracellular orientation change on the cell plasma membrane,so as to enhance NL1/NRXN3? interaction.Therefore,the enhancement of the interaction favors NL1's synaptogenic ability.As the extracellular stalk region widely exists in the transmembrane proteins,the principle of stalk-mediated interaction between transmembrane proteins and their ligands might be universal.In the third project,based on the general stalk-regulation principle,we found that an amino acid mutation in the transmembrane domain affects Fc?RIIB extracellular orientation through its stalk region.It leads to the weakening of the interaction between Fc?RIIB and Ig G ligands(Ig G1,Ig G2 and Ig G3,etc.)and finally causes the dysfunction of Fc?RIIB.In summary,the cell plasma membrane can affect the orientation change of transmembrane protein's extracellular domain through its two-dimensional confinement,bio-mechanical environment,membrane potential and its dynamic interaction with transmembrane protein,so as to regulate the interaction between transmembrane protein and its ligands.